PubMed Health⌕ Search

Biomedical subjects

P C Williamson

Publications and source records attributed to P C Williamson.

At least 19 recordsLinked to original sources
PubMed2001

The effect of vertical and horizontal head positioning in panoramic radiography on mesiodistal tooth angulations.

The purposes of this study were to examine the effect of potentially common patient positioning errors in panoramic radiography on imaged mesiodistal tooth angulations and to compare these results with the imaged mesiodistal tooth angulations present at an idealized head position. A human skull served as the matrix into which a constructed typodont testing device was fixed according to anteroposterior and vertical cephalometric normals. The skull was then repeatedly imaged and repositioned five times at each of the following five head positions: ideal head position, 5 degrees right, 5 degrees left, 5 degrees up, and 5 degrees down. The images were scanned and digitized with custom software to determine the image mesiodistal tooth angulations. Results revealed that the majority of image angles from the five head positions were statistically significantly different than image angles from the idealized head position. Maxillary teeth were more sensitive to 5 degrees up/down head rotation, with 5 degrees up causing mesial projection and 5 degrees down causing distal projection of maxillary roots. Mandibular anterior teeth were more sensitive to 5 degrees right/left head rotation, with the projected mesiodistal angular difference between 5 degrees right and 5 degrees left rotation ranging from 4.0 degrees to 22.3 degrees. Maxillary teeth were relatively unaffected by 5 degrees right/left head rotation, and mandibular teeth were relatively unaffected by 5 degrees up/down head rotation. It was concluded that the clinical assessment of mesiodistal tooth angulation with panoramic radiography should be approached with extreme caution with an understanding of the inherent image distortions that can be further complicated by the potential for aberrant head positioning.

Cephalometry↗
PubMed2001

Factors that relate to treatment duration for patients with palatally impacted maxillary canines.

The objectives of this study were to determine the relationship between the initial position of a palatally impacted maxillary canine (as seen on a panoramic radiograph) and the duration of orthodontic treatment and to determine whether a difference in treatment duration existed between patients with bilateral palatally impacted canines and patients with unilateral impaction. A total of 47 adolescent subjects were chosen (9 subjects with unilateral impactions and 18 subjects with bilateral impactions). All subjects had full fixed orthodontic appliances placed. The treatment duration of this group was compared with that of a control group with similar characteristics but without the impacted canine. The results showed that the average duration of treatment was 22.4 months for the control group, 25.8 months for the unilateral-impacted group, and 32.3 months for the bilateral-impacted canine group. The length of treatment for the impacted canine sample was related to the age of the patient at the start of treatment; younger patients required a longer treatment. The younger the patient, the more severely impacted the canine. The bilateral-impacted canine group had at least 1 canine that was more severely impacted than the impacted canine in the unilateral-impacted group. If the canine was impacted less than 14 mm from the occlusal plane, treatment duration averaged 23.8 months; if the canine was impacted more than 14 mm from the occlusal plane, treatment duration averaged 31.1 months.

Adolescent↗
PubMed2001

Neural correlates of traumatic memories in posttraumatic stress disorder: a functional MRI investigation.

OBJECTIVE: The neuronal circuitry underlying posttraumatic stress disorder (PTSD) was studied in traumatized subjects with and without PTSD. METHOD: Traumatized subjects with (N=9) and without (N=9) PTSD were studied by using the script-driven symptom provocation paradigm adapted to functional magnetic resonance imaging at a 4-T field strength. RESULTS: PTSD subjects showed significantly less activation of the thalamus, the anterior cingulate gyrus (Brodmann's area 32), and the medial frontal gyrus (Brodmann's area 10/11) than did the comparison subjects. CONCLUSIONS: The findings suggest anterior cingulate, frontal, and thalamic involvement in the neuronal circuitry underlying PTSD.

Adult↗
PubMed2001

Does sex influence the relation between symptoms and neurocognitive functions in schizophrenia?

OBJECTIVE: A secondary analysis of our data to investigate if sex influences the specificity of the relationship between each of the 3 clinical syndromes (i.e., reality distortion, disorganization and psychomotor poverty) in schizophrenia and the neurocognitive functions that are thought to represent regional brain functions. PATIENTS AND DESIGN: Fifty-seven male and 30 female patients with a DSM-III-R diagnosis of schizophrenia were rated on the Scale for Assessment of Negative Symptoms and the Scale for Assessment of Positive Symptoms to derive scores for psychomotor poverty, disorganization, and reality distortion syndromes. All subjects completed a battery of neuropsychological tests purported to assess functioning of left temporal, right temporal, left basal frontal, right basal frontal, and dorsolateral prefrontal cortex. RESULTS: Correlation coefficients between syndrome scores and neuropsychological measures showed only word fluency (left frontal functioning) to have a statistically significant association with psychomotor poverty in women (p < 0.01). This relation was specific to psychomotor poverty syndrome. No relations between neurocognitive measures and symptoms were seen in men. CONCLUSIONS: The lack of specific relations between symptom dimensions in schizophrenia may be influenced by the fact that the neuronal circuitry associated with particular symptom dimensions may differ in men and women.

Adult↗
PubMed2000

Comparison of the quantification precision of human short echo time (1)H spectroscopy at 1.5 and 4.0 Tesla.

Precise quantification of human in vivo short echo time (1)H spectra remains problematic at clinical field strengths due to broad peak linewidths and low signal-to-noise ratio (SNR). In this study, multiple STEAM spectra (TE = 20 ms, volume = 8 cm(3)) were acquired in a single individual at 1.5 T and 4 T to compare quantification precision. Test-retest STEAM spectra (volume = 1.5 cm(3)) were also acquired from the anterior cingulate and thalamus of 10 individuals at 4.0 T. Metabolite levels were quantified using automated software that incorporated field strength-specific prior knowledge. With the distinct methods of data acquisition, processing, and fitting used in this study, peak height SNR increased approximately 80% while peak linewidth increased by approximately 50% in the 8 cm(3) volumes at 4.0 T compared to 1.5 T, resulting in an average increase in quantification precision of 39%. Metabolite levels from test-retest data (1.5 cm(3) voxels at 4.0 T) were quantified with similar inter- and intraindividual variability. Magn Reson Med 44:185-192, 2000. Published 2000 Wiley-Liss, Inc.

Brain↗
PubMed2000

Spectroscopic lineshape correction by QUECC: combined QUALITY deconvolution and eddy current correction.

Lineshape distortion due to residual eddy currents and magnetic field inhomogeneities are often present in short echo time (1)H spectroscopic data. Lineshape correction methods such as QUALITY deconvolution and eddy current correction (ECC), which use a separate reference spectrum for lineshape correction, have shortcomings when unsuppressed water is chosen as the reference. This paper outlines a method of integrating both techniques to overcome these limitations while still using unsuppressed water as the reference signal. This hybrid lineshape correction technique (QUECC) is demonstrated in vivo using stimulated echo acquisition mode (STEAM) localized 4.0 Tesla data. Metabolite quantification precision increased by an average of 7%-46% compared to QUALITY deconvolution (depending on filtering) and by an average of 6% compared to ECC.

Humans↗
PubMed1999

A short echo proton magnetic resonance spectroscopy study of the left mesial-temporal lobe in first-onset schizophrenic patients.

BACKGROUND: Past 1H magnetic resonance spectroscopy (MRS) studies of the temporal lobe in schizophrenic patients have shown decreased levels of N-acetylaspartate (NAA) suggesting reduced neuronal density in this region. However, the measured volumes have been large and included contributions from mostly white matter. METHODS: Short echo 1H MRS was used to measure levels of NAA and other metabolites (i.e., glutamate and glutamine) from a 6 cm3 volume in the left mesial-temporal lobe of 11 first-episode schizophrenic patients and 11 healthy control subjects of comparable age, gender, handedness, education, and parental education levels. Spectra were quantified without operator interaction using automated software developed in our laboratory. Metabolite levels were normalized to the internal water concentration of each volume studied. Images were also obtained to determine temporal lobe gray and white matter volumes. RESULTS: No significant differences were found between levels of NAA or other metabolites, or gray and white matter volumes, in first-episode schizophrenic patients and comparison subjects. CONCLUSIONS: Since the volume studied was small compared to previous studies and contained mostly gray matter, this result suggests consequential NAA decreases may be restricted to regions of white matter.

Adolescent↗
PubMed1999

A 1H-decoupled 31P chemical shift imaging study of medicated schizophrenic patients and healthy controls.

BACKGROUND: Current 31P spectroscopy research in schizophrenia has examined phospholipid metabolism by measuring the sum of phosphomonoesters and the sum of phosphodiester-containing molecules. Proton decoupling was implemented to measure the individual phosphomonoester and phosphodiester components. This is the first study employing this technique to examine schizophrenic patients. METHODS: Multivoxel two-dimensional chemical shift in vivo phosphorous-31 magnetic resonance spectroscopy with proton decoupling was used to examine a 50-cm3 volume in prefrontal, motor, and parieto-occipital regions in the brain. Eleven chronic medicated schizophrenic patients were compared to 11 healthy controls of comparable gender, education, parental education, and handedness. RESULTS: A significant increase in the mobile phospholipid peak area and its full width at half maximum was observed in the medicated schizophrenic patients compared to the healthy controls in the prefrontal region. Inorganic orthophosphate and phosphocholine were lower in the schizophrenic group in the prefrontal region. CONCLUSIONS: The increased sum of phosphodiester [mobile phospholipid + glycerol-3-phosphoethanolamine (GPEth) + glycerol-3-phosphocholine (GPCh)] in schizophrenic patients, measured in earlier studies, arises from the phospholipid peak (MP) and not the more mobile phosphodiesters (GPEth, GPCh) as was originally suspected. A decrease in the phosphocholine component of the phosphomonoesters was also observed in the schizophrenic patients. These findings are consistent with an abnormality in membrane metabolism in the prefrontal region in schizophrenics.

Adult↗
PubMed1999

Factors affecting the quantification of short echo in-vivo 1H MR spectra: prior knowledge, peak elimination, and filtering.

Short echo 1H in-vivo brain MR spectra are difficult to quantify for several reasons: low signal to noise ratio, the severe overlap of spectral lines, the presence of macromolecule resonances beneath the resonances of interest, and the effect of resonances adjacent to the spectral region of interest (SRI). This paper outlines several different quantification strategies and the effect of each on the precision of in-vivo metabolite measurements. In-vivo spectra were quantified with no operator interaction using a template of prior knowledge determined by mathematically modeling separate in-vitro metabolite spectra. Metabolite level estimates and associated precision were compared before and after the inclusion of macromolecule resonances as part of the prior knowledge, and following two different methods of handling resonances adjacent to the SRI. The effects of rectangular and exponential filters were also investigated. All methods were tested using repeated in-vivo spectra from one individual acquired at 1.5 T using stimulated echo acquisition mode (STEAM, TE = 20 ms) localization. The results showed that the inclusion of macromolecules in the prior knowledge was necessary to obtain metabolite levels consistent with the literature, while the fitting of resonances adjacent to the SRI concurrent with modeled metabolites optimized the precision of metabolite estimates. Metabolite levels and precision were also affected by rectangular and exponential filtering, suggesting caution must be taken when such filters are used.

Animals↗
PubMed1999

Horizontal condylar angulation and condyle position associated with adolescent TMJ disk status.

The purpose of this research was to examine the relationship between horizontal condylar angulation and position and joint status in an adolescent population. Submentovertex (SMV) radiographs and MRI (magnetic resonance images) of 95 subjects (56 females and 39 males) between the ages of 10-17 years (mean age 13.3 years) were used for this study. Horizontal condylar angulation as well as A-P and transverse condyle position were determined in relation to a cranial base reference (a line formed between the two foramina spinosa) from SMV images. Joint status variables consisted of disk length and disk displacement measurements taken from medial, central and lateral sagittal MRI slices of each joint. Additional joint status variables were derived through a principal component analysis which was used to calculate a single disk length, disk displacement, and internal derangement variable for each joint. The results were: 1. No significant correlations (p = .05) were found between any of the joint status variables and horizontal condylar angulation; 2. Statistically significant correlations (r = .14 to .22, p = .05) were observed between certain joint status variables (anterior disk displacement in medial and central joint slices, disk displacement variable, and TMJ internal derangement variable) and transverse condyle position; and, 3. Statistically significant correlations (r = -.22 to .25; p = .05) were observed between condylar angulation and both A-P and transverse condyle position.

Adolescent↗
PubMed1999

Quantifying 1H decoupled in vivo 31P brain spectra.

Our objective was to develop a precise method for quantification of in vivo proton decoupled 31P spectra from the human brain. This objective required that an appropriate spectral model be created and that the quantification was performed using a non-subjective fitting technique. The precision of the quantification was assessed using Cramer-Rao standard deviations and compared using two different spectral models: one containing a pair of peaks representing 2,3-diphosphoglycerate, the other excluding this metabolite. The data was quantified using a Marquardt-Levenberg (ML) algorithm incorporating prior knowledge with a Hankel singular value decomposition (HSVD) performed initially to provide parameter estimates for the ML algorithm. Quantification was performed on two different in vivo 2-D CSI 31P data sets: the first examined 11 normal controls, the second examined a single individual six times. Spectra from a region in the parieto-occipital cortex were analyzed. The Cramer-Rao standard deviations were significantly lower for some metabolites with 2,3-diphosphoglycerate in the model: in the repeat study mobile phospholipids (p = 0.045) and phosphocholine (p = 0.034), and in the 11 controls mobile phospholipids (p = 0.003) and Pi (p = 0.002).

2,3-Diphosphoglycerate↗
PubMed1998

Landmark identification error in submentovertex cephalometrics. A computerized method for determining the condylar long axis.

The purpose of this study was to examine the identification error of certain submentovertex landmarks and to compare three different methods of determining horizontal condylar angulation in submentovertex radiographs. To determine landmark identification error, a random sampling of 12 submentovertex radiographs from preorthodontic patients between the ages of 10 and 17 years was used to determine both intraexaminer and interexaminer reliability. The error associated with the identification of each of 11 landmarks varied between specific landmarks, between the same landmarks bilaterally, and between the vertical and horizontal components of the same landmark. In general, intraexaminer data showed less landmark identification error in both vertical and horizontal directions than did interexaminer data. The foramen spinosum landmarks demonstrated the lowest identification error in both horizontal and vertical direction (intraexaminer), whereas greater identification error was associated with the condylar lateral poles and posterior condylar points (both intraexaminer and interexaminer). A comparison of three different methods of condylar angulation determination was undertaken through the use of two tracings of each of 101 submentovertex radiographs. A computer-derived method representing the principal axis of minimum moment of inertia of the condyle was shown to be more reliable (p < 0.05) with respect to describing condylar angulation than both a method that used a best-fit line through the anterior condylar border and an interpolar axis method.

Adolescent↗
PubMed1998

A short echo 1H spectroscopy and volumetric MRI study of the corpus striatum in patients with obsessive-compulsive disorder and comparison subjects.

OBJECTIVE: It is likely that the corpus striatum is involved in obsessive-compulsive disorder (OCD). Prior studies have inconsistently found alterations in caudate volumes in patients with OCD. This study was undertaken in the hope that N-acetylaspartate and volumetric measures together would elucidate the presence and nature of corpus striatum volumetric abnormalities in OCD. METHOD: Thirteen patients meeting the DSM-IV criteria for OCD, who had been medication free for a minimum of 6 weeks, and 13 psychiatrically normal matched comparison subjects participated in the study. Short echo 1H magnetic resonance spectroscopy (1H-MRS) was used to measure levels of N-acetylaspartate and several other cerebral metabolites from a 4.5-cm3 volume in the left corpus striatum of all 26 subjects. Metabolite levels were estimated by fitting the time domain spectroscopy data with a noninteractive computer program. Volumes of the left and right head of the caudate nucleus in each subject were determined by semiautomatic segmentation of the volumetric images. RESULTS: N-Acetylaspartate levels from the left corpus striatum were significantly lower in the patients with OCD than in the comparison subjects. There were no differences in either left or right caudate volume between the two groups. CONCLUSIONS: Despite the lack of differences in caudate volumes between the OCD patients and the comparison subjects, the lower level of N-acetylaspartate in the left corpus striatum of the patients suggests reduced neuronal density in this region. Inconsistent volumetric findings among prior studies may reflect a poorer sensitivity of magnetic resonance imaging morphometry for detecting neuronal loss compared with 1H-MRS measurement of N-acetylaspartate.

Adult↗
PubMed1997

Measurement of glutamate and glutamine in the medial prefrontal cortex of never-treated schizophrenic patients and healthy controls by proton magnetic resonance spectroscopy.

BACKGROUND: Positron emission tomographic and postmortem studies comparing schizophrenic patients with healthy control subjects have found medial prefrontal cortical and anterior cingulate abnormalities that suggest dysfunction in glutamatergic neurons. The glutamate used for nerve signal transduction is predominantly derived from glutamine. After signal transduction, glutamate released into the synapse is converted to glutamine in glial cells, transported back to the presynaptic neuron, and reconverted to glutamate for reuse. In this study, levels of glutamate and glutamine were examined by means of in vivo proton (1H) magnetic resonance spectroscopy. METHODS: Localized in vivo 1H spectra were acquired from a 4.5-cm3 volume in the left medial prefrontal cortex encompassing portions of Brodmann areas 24, 32, and 9 in 10 never-treated schizophrenic subjects and 10 healthy controls of comparable age, sex, handedness, education, and parental education. From each spectrum, metabolite levels were estimated for glutamate and glutamine, as well as 10 other metabolites and 3 macromolecules, by means of a noninteractive computer program that combined modeled in vitro spectra of every metabolite to reconstruct each in vivo spectrum. RESULTS: A significant increase in glutamine level was found in the medial prefrontal cortex of the schizophrenic patients compared with controls. N-acetylaspartate and other measured metabolites and macromolecules were not significantly changed in schizophrenics. CONCLUSION: Increased glutamine levels in the medial prefrontal region most likely reflect decreased glutamatergic activity in this region in never-treated schizophrenic patients compared with healthy controls.

Adolescent↗
PubMed1997

Neuropsychological correlates of syndromes in schizophrenia.

BACKGROUND: On the basis of Liddle's three-syndrome model of schizophrenia, it was predicted that: (1) symptoms of psychomotor poverty would be particularly correlated with impaired performance on neuropsychological tests likely to reflect functioning of the dorsolateral prefrontal cortex; (2) disorganisation would be particularly correlated with impaired performance on tests sensitive to medio-basal prefrontal functioning; and (3) reality distortion would be particularly correlated with measures sensitive to temporal lobe functioning. METHOD: The above hypotheses were tested on 87 subjects with a confirmed diagnosis of schizophrenia. Patients' symptoms were scored for each of the three syndromes. Patients completed six neuropsychological tests designed to measure impairment in specific areas of the brain. RESULTS: There was no support for the first two hypotheses. There was, however, evidence of a specific relationship between reality distortion and neuropsychological performance usually considered to be related to left temporal lobe functioning. CONCLUSIONS: Although not directly supporting the first two hypotheses; the results are, in general, consistent with there being different cortical-subcortical circuits associated with each of psychomotor poverty and disorganisation. Temporal lobe functioning appears to have particular significance for the reality distortion syndrome.

Adult↗
PubMed1997

EEG coherence and syndromes in schizophrenia.

BACKGROUND: Frith et al (1995) and others have hypothesised that disruptions in the connection between left frontal and temporal areas of the brain are a central deficit in schizophrenia. In this paper we examine whether such connectivity as assessed by EEG coherence is related to level of symptoms in patients with schizophrenia. METHOD: For 73 patients with schizophrenia, assessment of the EEG coherence between frontal and temporal regions were carried out under conditions of activation by a mathematical task, and between frontal and occipital regions when performing a visuo-spatial task. We then examined the relationship between these coherence measures and the reality distortion, disorganisation and psychomotor poverty dimensions of symptomatology. RESULTS: Only left frontal-temporal connectivity was found to have a significant negative relationship to symptomatology. This relationship was, however, specific to reality distortion rather than to symptoms of disorganisation or psychomotor poverty, and may be more characteristic of males than females. CONCLUSIONS: Disruption of frontal-temporal connectivity appears to have a specific relationship to reality distortion symptoms in schizophrenia.

Adult↗